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Re-Evaluating the Burden of Rabies in Africa and Asia Darryn L

Re-Evaluating the Burden of Rabies in Africa and Asia Darryn L

Re-evaluating the burden of in and Darryn L. Knobel,1 Sarah Cleaveland,1 Paul G. Coleman,2 Eric M. Fèvre,1 Martin I. Meltzer,3 M. Elizabeth G. Miranda,4 Alexandra Shaw,5 Jakob Zinsstag,6 & François-Xavier Meslin7

Objective To quantify the public health and economic burden of endemic canine rabies in Africa and Asia. Methods Data from these were applied to a set of linked epidemiological and economic models. The population at risk from endemic canine rabies was predicted using data on dog density, and human rabies were estimated using a series of probability steps to determine the likelihood of clinical rabies developing in a person after being bitten by a dog suspected of having rabies. Model outputs on mortality and morbidity associated with rabies were used to calculate an improved disability-adjusted life year (DALY) score for the disease. The total societal cost incurred by the disease is presented. Findings Human mortality from endemic canine rabies was estimated to be 55 000 deaths per year (90% confidence interval (CI) = 24 000–93 000). Deaths due to rabies are responsible for 1.74 million DALYs lost each year (90% CI = 0.75–2.93). An additional 0.04 million DALYs are lost through morbidity and mortality following side-effects of nerve-tissue vaccines. The estimated annual cost of rabies is US$ 583.5 million (90% CI = US$ 540.1–626.3 million). Patient-borne costs for post-exposure treatment form the bulk of expenditure, accounting for nearly half the total costs of rabies. Conclusions Rabies remains an important yet neglected disease in Africa and Asia. Disparities in the affordability and accessibility of post-exposure treatment and risks of exposure to rabid dogs result in a skewed distribution of the disease burden across society, with the major impact falling on those living in poor rural communities, in particular children.

Keywords Rabies/mortality/economics; Dogs; Cost of illness; Disability evaluation; Health care costs; Probability; Models, Theoretical; Africa; Asia (source: MeSH, NLM). Mots clés Rage (Maladie)/mortalité/économie; Chien; Coût maladie; Evaluation incapacité; Coût soins médicaux; Probabilité; Modèle théorique; Afrique; Asie (source: MeSH, INSERM). Palabras Rabia/mortalidad/economía; Perros; Costo de la enfermedad; Evaluación de la incapacidad; Costos de la atención en salud; Probabilidad; Modelos teóricos; África; Asia (fuente: DeCS, BIREME).

Bulletin of the Health Organization 2005;83:360-368.

Voir page 366 le résumé en français. En la página 366 figura un resumen en español.

Introduction These problems are not unique to rabies, and the recog- More than 99% of all human deaths from rabies occur in the nized poor quality of much public health information from developing world (1), and although effective and economical developing has prompted several investigations into control measures are available (2, 3) , rabies remains a neglected the distribution of major infectious diseases and the mortality disease throughout most of these countries (4, 5). A major fac- and morbidity attributable to them. Such studies are based on tor in the low level of political commitment to rabies control estimates of occurrence extrapolated from more readily quan- is a lack of accurate data on the true public health impact of tifiable determinants of disease, such as vector distribution or the disease. It is widely recognized that the number of deaths host immunity (8–10). For rabies, a similar predictive approach officially reported greatly underestimates the true incidence of has been used to estimate human deaths from rabies in the disease. Patients may not present to medical facilities for treat- United of using a probability decision tree ment of clinical disease; few cases receive laboratory confirma- method to determine the likelihood of clinical rabies develop- tion; and clinical cases are often not reported by local authorities ing in a person bitten by a dog suspected to be rabid (6). Dog to central authorities (1, 6, 7). bites are reported proportionately more frequently than human

1 Centre for Tropical Veterinary Medicine, Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush, Roslin, Midlothian EH25 9RG, Scotland. Correspondence should be sent to Dr Knobel at this address (email:[email protected]). 2 London School of Hygiene and Tropical Medicine, Keppel Street, London, England. 3 Centers for Disease Control and Prevention, Atlanta, GA 30333, USA. 4 Communicable Disease, Surveillance and Response, World Health Organization, Regional Office for the Western Pacific, , . 5 AP Consultants, Andover SP11 7BA, England. 6 Swiss Tropical Institute, Basel, Switzerland. 7 World Health Organization, Geneva, Switzerland. Ref. No. 03-008862 (Submitted: 16 February 2004 – Final revised version received: 3 July 2004 – Accepted: 5 July 2004)

360 Bulletin of the World Health Organization | May 2005, 83 (5) Research Darryn L. Knobel et al. Burden of rabies in Africa and Asia cases of rabies and may provide an accessible data source from rural dog-population densities (21–23), so the human popula- which human deaths from rabies can be inferred. tion considered to be at risk was calculated using the regional The objective of our study was to estimate the burden of rural ratios for to dogs. Implicit in this approach is rabies in Africa and Asia by applying data derived from these the assumption that all human urban populations are at risk regions to this model and to thereby present a data-driven in rabies-affected areas. assessment of the human and economic costs of rabies in the Four basic scenarios were considered (Africa and Asia, developing world. We define Africa as all countries both rural and urban); these reflect broad differences in fac- on the plus ; Asia is defined as those tors that influence rabies epidemiology and the treatment of countries falling under the WHO-defined South- people exposed to the disease. Initial parameter estimates were and Western Pacific Region, including Pakistan. Only derived following a review of the relevant literature, including countries considered by WHO and the Office International des publications from peer-reviewed journals and grey literature Epizooties as having endemic canine rabies were considered in sources. Parameter estimates and confidence distributions were this analysis. The list of all countries included in the study avail- then fixed using a three-stage consensus approach (as described in reference 9) within the WHO Burden of Rabies Working able from http://www.vet.ed.ac.uk/ctvm/Research/Appendices/ Group. First, a workshop was held during which parameter appendices.html. estimates were presented and discussed and preliminary predic- tions made using the model. Second, a comprehensive analysis Methods using agreed upon estimates was conducted, and the model was Human rabies deaths validated against known data. Third, each participant was sent Full details of the methods used in the dog-bite probability the results of this analysis, along with the data and assumptions. model have been published elsewhere (6). Briefly, the model These were reviewed and adjusted as appropriate before final recognizes that not all bites from rabid dogs result in infection agreement was reached. The final model parameter estimates and that not every infection leads to clinical signs and . and distributions are presented in Table 2 (web version only, One of the principal factors influencing the outcome of a bite available at: http://www.who.int/bulletin). from a rabid dog is the location of the bite on the body (11, For the analysis, Asia was subdivided into three units: 12). The model uses the distribution of injuries on the body , and Other Asia. Initial data sources and model together with the likelihood of the patient receiving successful validation indicated that parameter estimates for India and treatment to predict the outcomes of bites from rabid dogs. Other Asia were similar. However, preliminary model pre- The model thus allows the incidence of bites from suspected dictions for China overestimated the number of deaths by one order of magnitude when these same estimates were rabid dogs among the human population considered to be at used compared with the 1000 deaths suggested by expert risk to be used as a determinant of the number of human deaths opinion. The discrepancy is possibly explained by the use of from rabies. post-exposure treatment in China: the accounts for The human population at risk from canine rabies was two-thirds (5 million cases) of total post-exposure treatment taken as the number of people living in areas affected by ca- (PET) used in Asia (24), and the locally-produced tissue-culture nine rabies where the density of the dog population exceeds vaccine is safe and relatively inexpensive (25). These factors the threshold density at which canine rabies is capable of be- suggest that PET for rabies is more accessible and utilized more ing maintained endemically. Dog-population densities were frequently in China than in the rest of Asia. To account for this inferred from human densities derived from two regional in the model, the probability of a person bitten by a suspected population density datasets (13, 14) with adjustments made rabid dog and receiving PET was assumed to be equally high to account for (15). Associated dog-popula- in both urban and rural settings in China (minimum = 95%; tion numbers were calculated by dividing human figures by most likely = 97%; maximum = 100%). In light of the paucity of the regional average ratio of humans to dogs, based on values data for China, the model’s predictions for this country should given in Table 1. The threshold density for rabies persistence be treated with caution. was taken as 4.5 dogs/km², based on predictions produced from The model was arrayed as a spreadsheet template (using data on rabies in rural (16); these data are Microsoft Excel 2000, Microsoft Inc., Redmond, WA). Uncer- consistent with empirical observations from elsewhere in Africa tainty in parameter estimates, and inherent parameter vari- (17–20). This density falls within the range of estimates of ability due to between-country differences, were incorporated

Table 1. Mean human:dog ratio for Africa and Asia (determined from sources available from: http://www.vet.ed.ac.uk/ctvm/Research/ Appendices/appendices.html)

Regiona Human:dog ratio Africa Asia China Urban Rural Urban Rural Urban Rural Mean ratiob 21.2 (12.5–37.1) 7.4 (5.7–9.7) 7.5 (4.8–10.1) 14.3(0–45.0) NAc NA Mean ratio for region 12.3 (11.2–20.6) 9.5 (4.5–14.6) 48.3 (0–147.0)

a Insufficient data were available to calculate a separate figure for India and for rural China versus urban China. b Figures in parentheses are 95% confidence intervals. c NA = not available.

Bulletin of the World Health Organization | May 2005, 83 (5) 361 Research Burden of rabies in Africa and Asia Darryn L. Knobel et al.

Table 4. Direct (medical) post-exposure treatment costing data and sources (available from: http://www.vet.ed.ac.uk/ctvm/Research/ Appendices/appendices.html)

Estimate Parameter Africa Asia Source Patient numbers No. PETa cases per year 200 000 7 500 000 11–14, 23–27 No. (%) PET patients receiving tissue-culture vaccines 180 000 (90) 5 025 000 (67) 11–14, 23–27 No. (%) of patients receiving tissue-culture vaccine intramuscularly 180 000 (100) 4 874 250 (97) 11–14, 23–27 No. (%) of patients receiving tissue-culture vaccine intradermally 0 (0) 150 750 (3) 11–14, 23–27 No. (%) PET patients receiving nerve-tissue vaccines 20 000 (10) 2 475 000 (33) 11–14, 23–27 No. (%) PET patients receiving rabies immunoglobulin 2 000 (1) 450 000 (6) 11–14, 23–27 No. (%) PET patients receiving human rabies immunoglobulin 0 (0) 45 000 (10) No. (%) PET patients receiving equine rabies immunoglobulin 2 000 (100) 405 000 (90) Costs Common costs Material costs per injection (includes needles, syringes, swabs, etc.) US$ 0.10 E. Miranda unpublished data, 2003 Overhead costs per PET visit (includes anti-rabies staff US$ 0.50 39 salaries and administration costs) Tissue-culture vaccine costs Intramuscular vaccination Vaccine cost per dose US$ 10.00 WHO Procurement Services, personal communication, 2003 Visits per patient 3 40 Injections per patient 3 Assuming standard Essen regimen Intradermal vaccination Vaccine cost per dose US$ 2.50 WHO Procurement Services, personal communication, 2003 Visits per patient 3 E. Miranda unpublished data, 2003 Injections per patient 6 Assuming Thai Red Cross regimen Nerve-tissue vaccine costs Vaccine cost per dose US$ 0.40 7 Visits per patient 7 33 Injections per patient 7 Assuming standard regimen Rabies immunoglobulin Human rabies immunoglobulin cost per dose US$ 110.00 WHO Procurement Services, personal communication, 2003 Equine rabies immunoglobulin cost per dose US$ 25.00 WHO Procurement Services, personal communication, 2003

a PET = post-exposure treatment. into the model by assigning confidence distributions to input were considered: a direct DALY score derived from mortality parameters. Parameter distributions were sampled iteratively due to the disease and an indirect DALY score, taking into ac- (until convergence at < 1.5%) using a Monte Carlo simulation count morbidity and mortality following side-effects of nerve- procedure (@Risk Pro 4.5, Palisade Corp., Newfield, NY). Model tissue vaccines. predictions are reported using the means of the resulting prob- ability distributions, with the 5th and 95th percentiles (90% Direct DALY score confidence intervals) as the lower and upper bounds, respectively. The output of the predictive model provided the estimated A full account of the technical details of the model, including annual number of deaths due to rabies. Age-structures and sex- results of the sensitivity analysis, is available from: http://www. structures of rabies cases were obtained from seven reported vet.ed.ac.uk/ctvm/Research/Appendices/appendices.html. studies (27–33). All parameter estimates and data sources re- lated to the calculation of the rabies DALY score are given in Disability-adjusted life year score Table 3 (web version only, available at: http://www.who.int/ The disability-adjusted life year (DALY) score is a standardized, bulletin). Using these parameter estimates, a DALY score for comparative measure of the burden of disease. The DALY score rabies was determined using previously described methods (26, for a particular condition is a composite score of the years of 34). Parameter variability was again incorporated by assign- life lost (YLL) due to premature mortality and the years of life ing confidence distributions and using simulation software as lived with a disability (YLD) caused by the condition (26). To described above. The 5th and 95th percentiles were used as the calculate a DALY score for rabies the following components lower and upper bounds for the predicted scores.

362 Bulletin of the World Health Organization | May 2005, 83 (5) Research Darryn L. Knobel et al. Burden of rabies in Africa and Asia Indirect DALY burden a result of the disease. The costs due to rabies were considered Evidence suggests that non-rabies induced morbidity and mor- under the following categories: tality may constitute a sizeable proportion of the rabies burden • direct (medical) human costs from post-exposure treatment in developing countries. Approximately one-third of all human • indirect (patient) costs from post-exposure treatment rabies post-exposure treatments are carried out using crude • costs to control rabies among dogs nerve-tissue vaccines (35), despite the occurrence of severe and • livestock losses sometimes fatal allergic encephalomyelitic reactions (36–38). • surveillance costs. Nerve-tissue vaccines were classified into two groups based on differing incidence rates and clinicopathological signs of Table 4 and Table 5 give a breakdown of the costing data used adverse reactions (37, 38). These were the Semple type (made in the economic analysis. from phenol-treated sheep-brain or goat-brain tissue) and vac- For this analysis, direct medical costs included the cost of cines derived from suckling-mouse brain. For the purpose of biologicals (rabies vaccines and immunoglobulin) and the cost this preliminary analysis, disability weights for post-vaccination of their administration, including materials and staff salaries. neurological reactions, used in the calculation of the YLDs, were Indirect costs included out-of-pocket expenses for patients, taken as those reported for similar conditions by Murray & such as transport costs to and from rabies-treatment centres, Lopez (39) (Table 3). The use of equivalent disability weights and loss of income while receiving treatment (40). Costs asso- represents an admittedly crude first attempt to determine a ciated with the treatment of dog bites and the administration YLD component of the DALY score for rabies; future attempts of antibiotics and tetanus immunizations were not included. would benefit from a formal disability weighting procedure. Due to the erratic of reporting, national numbers of patients receiving post-exposure treatment annually were aver- The economic burden of rabies aged over a period of 5 years (1996–2000). Countries for which The mortality rate and DALY score provide estimates of the no reports could be found for this period were considered not to burden of disease on human health. A second component of have treated any patients. Post-exposure treatment was catego- the impact of disease is the economic cost incurred by society as rized by administration route (intramuscular or intradermal) on

Table 5. Indirect (patient) costs of post-exposure treatment and other costs associated with rabies. Data sources are available from: http://www.vet.ed.ac.uk/ctvm/Research/Appendices/appendices.html

Estimate Parameter Africa Asia Source Indirect PETa costs No. of PET patient visits 680 000 32 400 000 Calculated from Table 4 Proportion of visits accompanied by an adult 0.4 0.4 2, 16 Total No. of visits (patients plus those accompanying them) 952 000 45 360 000 Calculated Income loss No. of working days lost per person per PET visit 0.5 0.5 15 Daily per capita Gross National Income US$ 1.87 US$ 3.50 41 Income loss per person per PET visit US$ 0.94 US$ 1.75 Calculated Transport costs Transport costs per person per visit US$ 2.00 US$ 3.80 40, M. Kaare, personal communication, 2002 Dog rabies costs Vaccination costs No. dogs vaccinated annually 6 700 000 40 000 000 11–14, 23–27 Cost per dog vaccinated US$ 1.30 US$ 1.30 42 Population control costs No. dogs killed annually 200 000 5 000 000 11–14, 23–27 Cost per dog killed US$ 5.00 US$ 5.00 43

Livestock losses Total no. 230 000 000 423 000 000 44 Rabies incidence rate/100 000 cattle 5 5 11–14, 23–27 Annual no. of cattle deaths from rabies 11 500 21 150 Calculated Cost per head of cattle US$ 150.00 US$ 500.00 A. Shaw, unpublished data, 2002

Surveillance costs No. rabies diagnostic tests per year 5 300 16 500 11–14, 23–27 Cost per test US$ 5.68 US$ 5.68 45

a PET = post-exposure treatment.

Bulletin of the World Health Organization | May 2005, 83 (5) 363 Research Burden of rabies in Africa and Asia Darryn L. Knobel et al.

Table 6. Estimated human mortality caused by canine rabies in Africa and Asia

Asia Model output India China Other Asia Africa Urban Rural Urban Rural Urban Rural Urban Rural Total population (millions) 284.7 732.2 459.1 816.1 295.7 525.4 294.2 498.1 Population at risk (millions) 284.7 710.4 459.1 498.3 295.7 409.1 294.2 340.1 No. bites from suspected rabid dogs (thousands) 409.4 893.4 660.1 626.7 425.2 514.5 374.3 427.8 No. of rabies deathsa 1 058 18 201 1 324 1 257 853 8 135 5 886 17 937 No. deaths/100 000 people 0.37 2.49 0.29 0.15 0.29 1.55 2.00 3.60 No. subregional deathsb 19 713 2336 9 489 (4 192–39 733) (565–5 049) (2 281–19 503) No. regional deaths 31 539 (8 149–61 425) 23 705 (6 903–45 932) Total no. deaths 55 270 (23 910–93 057) Overall no. deaths/100 000 people 1.38 (0.60–2.33) Predicted deaths in the absence of any 327 160 (166 904–525 427) post-exposure treatment

a Rabies deaths are the means of output probability distributions calculated independently and may therefore not sum exactly. b Figures in parentheses are the 5th and 95th percentiles of output probability distributions. the basis that intradermal vaccination reduces costs by 60–80% and 9.7% in Asia); this figure was then applied to all countries compared to the standard intramuscular regimen (41, 42). The in the region to predict the total number of dogs vaccinated. total number of vaccine doses (i.e. injections) administered and Cost predictions were based on the use of a central-point vac- the total number of visits made to rabies-treatment centres were cination system. Vaccination costs per dog include all com- derived from national estimates of the proportion of patients ponents of campaign organization, public awareness efforts, receiving treatment who were vaccinated with each schedule, and biological and material costs. Indirect costs borne by dog after adjustment to account for patient drop-out during the owners were not included in the analysis. course of treatment. Few published accounts dealing with Livestock losses to rabies can be significant; however, there treatment-seeking behaviour and compliance could be found are few published estimates of rabies incidence in livestock. Sub- so conservative estimates were made on the average number of mission of cattle specimens to central veterinary laboratories visits per schedule: 3 instead of 5 for the Essen and Thai Red reveals an annual incidence of 0.5–2 deaths/100 000 head of Cross regimens and 7 instead of 10–21 for the nerve-tissue cattle; this is certain to be a gross underestimate. Assuming a vaccine schedules. The proportion of patients receiving the rate of underreporting of 10, and using the lower end of the Zagreb schedule, based on available data, was negligible at the range of incidence rates to exclude transmission from scale of this study. It was assumed that all children aged < 16 reservoirs, an estimated incidence of 5 deaths/100 000 cattle years were accompanied by an adult. Assessment of transport is obtained. costs and income loss include costs to both patients and those Insufficient data were available to enable parameter vari- accompanying them. ability to be explicitly incorporated into the economic analysis. Annual dog vaccination figures could not be found for all An attempt was made to model the uncertainty surrounding countries so the average vaccination coverage of the estimated parameter estimates by inputting estimates as triangular dis- national dog population was calculated for those countries that tributions (43), with the maxima and minima set as ± 10% of submitted reports between 1996 and 2000 (10.3% in Africa each parameter’s values.

Table 7. Estimated disability-adjusted life year (DALY) score for rabies in Africa and Asia

DALY scorea Component Africa Asia Total Rabies deathsb 747 558 (217 690–1 448 514) 994 607 (257 275–1 939 125) 1 743 015 (754 019–2 934 656) Nerve-tissue vaccine reactions 360 (142–586) 44 525 (17 585–72 575) 44 885 (17 727–73 162) Total 747 918 (217 954–1 449 014) 1 039 119 (302 324–1 983 646) 1 787 886 (799 615–2 984 109) Total (assuming no post- 9 504 237 (4 848 684–15 264 050) exposure treatment)

a DALY scores are the means of output probability distributions calculated independently and may therefore not sum exactly. b Figures in parentheses are the 5th and 95th percentiles of output probability distributions.

364 Bulletin of the World Health Organization | May 2005, 83 (5) Research Darryn L. Knobel et al. Burden of rabies in Africa and Asia Results receiving post-exposure treatment is 1.25 million which is four Model outputs times lower than national estimates of 5 million; the predicted number of deaths remains more than double that estimated The results of the predicted human mortality, disability- adjusted life year score and economic burden of rabies are by expert opinion. However, recent figures communicated presented in Table 6, Table 7 and Table 8, respectively. The pre- by the Chinese authorities are more in line with the model’s dicted number of human deaths remained within the reported predictions (Personal communication, 2004): more than 2000 confidence limits when the threshold dog density was cases of rabies in humans were reported in 2003, with an 80% doubled to 9 dogs/km² (46 000; 90% confidence interval increase in the first quarter of 2004 (compared to the same (CI) = 19 000–79 000). Setting the threshold density to period in 2003). Given the gross underreporting associated 0 (i.e. assuming that all people are at risk within areas with rabies deaths, this suggests that the model may in fact be where canine rabies is endemic) also had little effect on the an underestimate of the true number, and the original predic- model: in such a scenario the predicted number of deaths tion of approximately 10 000 deaths may prove more realistic. was 67 000 (90% CI = 30 000–110 000). Detailed studies on dog and rabies epidemiology and treatment in China are necessary to resolve this. Discussion WHO’s 1999 World survey of rabies (35) reported 1722 human rabies deaths from the study regions: 147 in Africa and This paper provides the results of the first attempt at a quan- 1575 in Asia. The predicted figure of 55 000 deaths suggests titative prediction of the burden of rabies in Africa and Asia. that only 3% of human rabies deaths are recorded by central Although we attempted to incorporate the entire range of health authorities, a rate of underreporting of between 20 parameter variability, the final result is still likely to be an un- times (Asia) and 160 times (Africa). This is in agreement with derestimate of total mortality and morbidity caused by rabies in findings from other studies using active surveillance methods these regions. Only deaths due to canine rabies were assessed, that found the incidence of human rabies is up to 100 times omitting that fraction of human cases resulting from exposure to rabid wild animals (35). In determining the number of hu- greater than what is officially recorded (6, 47). mans at risk, only populations in areas where canine rabies is The burden of rabies is not evenly distributed across all endemic were included. This ignores the possibility of sporadic sectors of society but is influenced by age-related and socioeco- outbreaks in areas of low dog density or the introduction of nomic factors. The total cost (direct medical costs and indirect the virus into a previously rabies-free population, as happened patient costs, excluding those of any accompanying people) of on the Indonesian of Flores in 1997 (44). an average post-exposure treatment course as determined in The results of the modelling are consistent with those of this study is US$ 39.57 in Africa and US$ 49.41 in Asia. This other studies that have estimated the true incidence of rabies at amounts to a substantial fraction of annual per capita gross a national level. The recent national survey by the Association national income (GNI): 5.80% for the average person living in for the Prevention and Control of Rabies in India (45) esti- Africa and 3.87% for someone living in Asia. Even if medical mated a total of 18 500 human deaths from rabies in the coun- costs are fully subsidized by the government, out-of-pocket pa- try each year, which is close to the predicted figure of 19 700 tient expenses still comprise 1.5–2% of per capita GNI. Often in this report. The model also estimated the annual number government subsidies extend only to the provision of cheaper of patients receiving post-exposure treatment in India as 1.07 nerve-tissue vaccines, with tissue-culture vaccines being pro- million, which again is in good agreement with the reported vided only to those patients able to pay for them. There is there- national estimate of 1.1 million (46). The model’s predictions fore an income-related risk factor in exposure to the side-effects for China are less consistent: the predicted number of patients of nerve-tissue vaccines. This is compounded by occupational

Table 8. Estimated annual expenditure due to rabies

Costa Category Africa Asia Total PET costsb, c 9.1 (8.2–10.0) 475.9 (435.0–520.5) 485.0 (443.4–530.1) Direct (medical) 5.9 (5.2–6.6) 190.3 (171.4–210.5) 196.2 (176.9–216.7) Indirect (patient) 3.2 (2.9–3.5) 285.6 (259.2–312.1) 288.7 (262.2–315.4) Income loss 1.3 (1.2–1.4) 113.5 (104.4–122.9) 114.7 (105.7–124.1) Transport costs 1.9 (1.7–2.1) 172.1 (154.1–190.5) 174.0 (155.9–192.5) Dog rabies control costs 9.7 (8.8–10.6) 77.0 (71.5–82.3) 86.7 (80.7–92.8) Vaccination costs 8.7 (7.8–9.6) 52.0 (47.1–57.0) 60.7 (55.4–66.3) Population control costs 1.0 (0.9–1.1) 25.0 (22.5–27.5) 26.0 (23.4–28.6) Livestock losses 1.7 (1.5–1.9) 10.5 (9.4–11.8) 12.3 (11.0–13.7) Surveillance costs 0.03 (0.026–0.032) 0.09 (0.08–0.10) 0.12 (0.11–0.13) Total 20.5 (19.3–21.8) 563.0 (520.0–605.8) 583.5 (540.1–626.3)

a Costs are in millions of US$. b PET = post-exposure treatment. c Figures in parentheses are the 5th and 95th percentiles of output probability distributions.

Bulletin of the World Health Organization | May 2005, 83 (5) 365 Research Burden of rabies in Africa and Asia Darryn L. Knobel et al. and socioeconomic risk factors in the initial exposure to infec- to be the most cost-effective in the medium–long term (4); tion, further skewing the burden of rabies towards those sectors costs are typically recouped within 5–10 years, mainly through of society least able to bear it (45, 48). The results of our study decreased expenditure on human post-exposure treatment. O predict that there will be five times more rabies deaths in rural areas than in urban areas. Children in particular are at a higher Acknowledgements risk of exposure to rabid dogs. Typically, 30–50% of those re- The authors thank Dr Alex Wandeler and Dr Ursula Kayali for ceiving post-exposure treatment are children aged < 16 years their comments on an earlier draft of this manuscript and Dr (6, 49). Children are also more likely to suffer multiple bites Deborah Briggs for useful discussions. and bites to the face and head, both of which carry a higher risk of contracting rabies (31, 50). Funding: DK and SC are supported by a grant from the Well- Rabies continues to impact human health despite the come Trust. JZ is supported by NCCR “North-South” IP-4, existence of proven cost-effective control measures. Vaccinating which is funded by the Swiss National Science Foundation and domestic dogs against rabies results in a significant reduction in the Swiss Development Cooperation. the incidence of bites among the human population from dogs suspected to be rabid, and this control strategy has been shown Competing interests: none declared.

Résumé Réévaluation de la charge que représente la rage en Afrique et en Asie Objectif Quantifier le fardeau économique et la charge pour de 1,74 million d’années de vie ajustées sur l’incapacité perdues la santé publique que représente la rage canine endémique en chaque année (IC à 90% = 0,75-2,93). Quelque 0,04 million Afrique et en Asie. d’années de vie ajustées sur l’incapacité supplémentaires sont Méthodes Les données provenant de ces régions ont été en outre perdues du fait de la morbidité et de la mortalité dues appliquées à un ensemble de modèles épidémiologiques et aux effets secondaires des vaccins préparés sur tissu nerveux. Le économiques associés. On a estimé le nombre de personnes qui coût annuel estimatif de la rage est de US$ 583,5 millions (IC seraient exposées à la rage canine endémique à partir des données à 90% = US$ 540,1 – 626,3 millions). Le coût des traitements de la densité canine et le nombre des décès humains dus à la post-exposition supporté par les malades constitue l’essentiel des rage au moyen d’un modèle de probabilité pas à pas utilisé pour dépenses, soit près de la moitié du coût total de la rage. déterminer la probabilité qu’une personne mordue par un chien Conclusion La rage reste une maladie importante mais négligée présumé enragé présente la maladie. La mortalité et la morbidité en Afrique et en Asie. Les écarts aux plans de l’accessibilité liées à la rage fournies par les modèles ont été utilisées pour affiner financière et physique du traitement post-exposition et du risque le calcul des années de vie ajustées sur l’incapacité (DALY) pour la d’exposition aux chiens enragés rendent inégale la distribution maladie. Le coût social total de la maladie est présenté. de la charge de morbidité dans la société, les personnes les Résultats On a estimé à 55 000 [intervalle de confiance (IC) à plus touchées étant les habitants des communautés rurales 90% = 24 000-93 000] le nombre annuel des décès humains dus à défavorisées, et en particulier les enfants. la rage canine endémique. Les décès dus à la rage sont responsables

Resumen Reevaluación de la carga de rabia en África y Asia Objetivo Cuantificar la carga que supone la rabia canina endémica (IC) del 90% = 24 000-93 000). Las defunciones por rabia causan en África y Asia en términos económicos y de salud pública. unas pérdidas de 1,74 millones de AVAD cada año (IC90% = 0,75- Métodos Se aplicaron datos de esas regiones a un conjunto de 2,93). Otros 40 000 AVAD se pierden como consecuencia de la modelos epidemiológicos y económicos relacionados. La población morbilidad y mortalidad asociadas a los efectos colaterales de las humana expuesta al riesgo de sufrir rabia canina endémica se vacunas obtenidas con tejido nervioso. El costo anual estimado de predijo a partir de los datos disponibles sobre la densidad de perros, la rabia asciende a US$ 583,5 millones (IC90% = US$ 540,1 - 626,3 y las defunciones por rabia humana se estimaron usando una serie millones). Los costos del tratamiento postexposición asumidos por de pasos probabilísticos para determinar el riesgo de aparición los pacientes constituyen el grueso del gasto correspondiente, pues de rabia clínica en una persona que hubiera sido mordida por un suponen casi la mitad del costo total de la rabia. perro sospechoso de albergar rabia. Los resultados modelizados Conclusión La rabia sigue siendo una importante y sin embargo sobre la mortalidad y la morbilidad asociadas a la rabia se usaron descuidada enfermedad en África y Asia. Las disparidades en la para obtener un valor mejorado de los años de vida ajustados en asequibilidad y accesibilidad del tratamiento postexposición y en el función de la discapacidad (AVAD) para la enfermedad. Se presenta riesgo de exposición a perros rabiosos se traducen en una distribución el costo social total asociado a esta dolencia. asimétrica de la carga de morbilidad en la sociedad, de tal manera Resultados La mortalidad humana por rabia canina endémica se que el impacto principal de la enfermedad recae en los habitantes de estimó en 55 000 defunciones anuales (intervalo de confianza las comunidades rurales pobres, sobre todo en los niños.

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Table 2. Parameter estimates, probability distributions and data sources used in the prediction of human deaths from rabies from injury data on dog bites (data sources available from: http://www.vet.ed.ac.uk/ctvm/Research/Appendices/appendices.html)

Parameter estimates Param- Description Probability Africa Asia Source eter distribution of data Urban Rural Urban Rural Annual incidence of Trigen:a 1–6 suspect bites from Practical minimum 6 6 50 15 rabid dogs per Most likely 100 100 120 100 100 000 humans Practical maximum 227 227 250 250 Bottom and top percentiles 0%; 95% 0%; 95% 5%; 95% 5%; 95% P10 Probability of an Trigen: 2, 7 individual bitten by a Practical minimum 0.80 0.55 0.95 0.70 dog suspected to be Most likely 0.85 0.60 .097 0.75 rabid receiving Practical maximum 0.90 0.60 1.00 0.80 successful post- Bottom and top percentiles 5%; 95% 5%; 95% 10%; 100% 10%; 90% exposure treatment P1 Probability of a Beta:b India Other Asia 2, 3, 8–15 suspected rabid dog No. of suspect dogs examined 9 285 5 863 59 588 being confirmed No. confirmed rabid 5 291 2 906 22 923 rabid on laboratory P1 0.64 0.50 0.38 diagnosis P2 Probability of a bite Point probability 0.07 2, 16, 17, to the head or neck E. Miranda unpublished data, 2003 P3 Probability of a bite to Point probability 0.38 2, 16, 17, the upper extremity E. Miranda (arm or hand) unpublished data, 2003 P4 Probability of a bite Point probability 0.06 2, 16, 17, injury to the trunk of E. Miranda the body unpublished data 2003 P5 Probability of a bite to Point probability 0.49 2, 16, 17, the lower extremity E. Miranda (leg or foot) unpublished data, 2003 P6 Probability of Triangular: 18–21 developing rabies Minimum 0.30 following a bite to the Most likely 0.45 head by a rabid dog Maximum 0.60 P7 Probability of Triangular: 18–21 developing rabies Minimum 0.15 following a bite to an Most likely 0.28 upper extremity by a Maximum 0.40 rabid dog P8 Probability of Triangular: 18–21 developing rabies Minimum 0 following a bite to the Most likely 0.05 trunk by a rabid dog Maximum 0.10 P9 Probability of Triangular: 18–21 developing rabies Minimum 0 following a bite to a Most likely 0.05 lower extremity by Maximum 0.10 a rabid dog

a The Trigen distribution avoids the use of absolute maxima and minima by allowing the specification of a likely range for the parameter together with an estimation of the probability that the parameter will fall outside this range (top and bottom percentiles). b The Beta distribution is a binomial process allowing estimation of the probability of success p, given s successes from n trials. Assuming a non-informative Uniform (0, 1) prior, the Beta distribution takes the form p = Beta (s + 1, n – s + 1). See reference 22 for a discussion of commonly used probability distributions.

Bulletin of the World Health Organization | May 2005, 83 (5) A Research Burden of rabies in Africa and Asia Darryn L. Knobel et al.

Table 3. Parameter estimates and data sources used to calculate the disability-adjusted life year (DALY) score for rabies (data sources available from: http://www.vet.ed.ac.uk/ctvm/Research/Appendices/appendices.html)

Estimate Parameter Africa Asia Source No. human rabies deaths per yeara 23 788 (7 280–44 112) 30 942 (6 017–61 657) Model output (Table 3) No. PETb cases per year 200 000 7 500 000 12–14, 23–27 No. (%) of PET patients receiving nerve-tissue vaccines 20 000 (10) 2 475 000 (33) 12–14, 23–27 No. (%) of NTVc patients receiving Semple-type 16 000 (80) 1 980 000 (80) 12–14, 23–27 nerve-tissue vaccine No. (%) of NTV patients receiving suckling-mouse brain 4 000 (20) 495 000 (20) 12–14, 23–27 nerve tissue vaccine Rate of neurological complications per 100 patients Triangular: 16, 28–31 receiving Semple vaccine Minimum = 0.035; Most likely = 0.40; Maximum = 0.83 Case–fatality rate for cases of Semple neurological 0.17 30, 32, 33 complications Disability weight for Semple neurological complications 0.613 34 (disability weight for an episode of bacterial meningitis) Disability duration for Semple neurological complications Triangular: 35 Minimum = 1 day; Most likely = 8 days; Maximum = 1 year Rate of neurological complications per 100 patients Triangular: 29, 31, 35, 36 receiving suckling-mouse brain vaccine Minimum = 0.013; Most likely = 0.03; Maximum = 0.08 Case–fatality rate for cases of neurological complications 0.22 29 from suckling-mouse brain vaccine Disability weight for suckling-mouse brain neurological 0.725 34 (disability weight complications for an injured spinal cord) Disability duration for suckling-mouse brain neurological 200 days 37 complications DALY formula parameters Discount rate r 0.03 38 Age-weighting correction constant C 0.1658 38 Age-weighting function constant 0.04 38

a Values in parentheses are 90% confidence intervals. b PET = post-exposure treatment. c NTV = nerve-tissue vaccine.

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